ISSN:
0449-2951
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Rabesiaka and Kovacs have reported experiments in which the shapes of crystallization isotherms of several polyethylenes depended on the sample history as well as the intrinsic properties of the polymers. The suggestion was made that, in general, molten polyethylene is not in a true thermodynamic equilibrium and includes some quasi-indestructible clusters, which act as heterogeneous nuclei in the crystallization process. This paper reports anomalous brittleness temperature experiments on polyethylenes, the results of which are explainable in terms of quasi-indestructible clusters. The data are consistent with the supposition that the crystalline embryos responsible for the observed behavior result from strong entanglements or cross-linking in natural polyethylene and from binding to carbon black surfaces in black compounds. At the low, nonuniform shear rates in compression molding these clusters may survive relatively intact. If subsequent remelting is performed in the absence of shear, any ordered structure between entanglement points will expand but not break. Such configurations can contract to form crystalline embryos as the polymer is cooled.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1963.100010625
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